On 2/4/2017 12:41, Stefan Fuhrmann wrote: > On 31.01.2017 10:09, Stefan wrote: >> Hi, >> >> I've been looking at the cause of a deadlock when running ra-test.exe >> with -fs-type=fsx (trunk version). >> >> The most important findings are summed up here atm [1]. >> >> The issue was discussed with brane and danielsh on IRC (thanks for your >> time, once again). >> >> As far as my current understanding of the problem goes: the deadlock is >> caused by the fact that the apr_terminate() function registered in >> svn_cmdline_init() via the atexit-call is called after the termination >> of the threads which were created as part of the calls to >> apr_thread_pool_push() in svn_fs_x__batch_fsync_run(). >> >> This means that apr's thread counter (thd_cnt) is getting out of sync >> (since the apr-function thread_pool_func() is not executed) and then >> gets stuck in thread_pool_cleanup() (waiting for the already terminated >> threads to be terminated). >> >> To me it looks like svnserve's main-function already contains a >> safeguard against a corresponding issue, and calls >> apr_thread_pool_destroy(threads) (or was this a completely different >> scenario?). This however does not cover the threads created from >> svn_fs_x__batch_fsync_run(). >> >> Talking to danielsh and brane it became apparent to me that the issue >> might not be too obvious (in the end it might still be an issue on how I >> build SVN and therefore cause the atexit-registered apr_terminate() >> function to be called too late). It's also not fully clear to me at >> which exact point (in regards to registerd atexit()-calls) threads of >> the process are terminated if the process itself terminates. If indeed >> atexit()-registered functions get called after the threads are forcibly >> terminates (which to me it looks like it does atm) it might contradict >> the C(89/99) standard - see[2] 7.20.4.2/7.20.4.3. On the other side this >> thread on stackoverflow [3] suggests it's simply undefined (by the >> standard) what comes first. >> >> As danielsh suggested, I'm planning to come up with a plain minimal >> repro app only based on APR demonstrating the problem, so to make it >> more obvious (and double check for myself) what the issue is about. >> >> Regards, >> Stefan >> >> [1] http://www.luke1410.de:8090/browse/MAXSVN-94 >> [2] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf >> [3] >> https://stackoverflow.com/questions/39655868/what-does-the-posix-standard-say-about-thread-stacks-in-atexit-handlers-what >> > Hi Stefan, > > I had a look at the code and found a possibly related problem. > If you are using DLLs, this might have affected you. > > It would be nice if you could try r1781657 and see whether it > makes any difference in your case. > > -- Stefan^2.
Hi Stefan^2, I tested trunk r1781790 which also includes your follow-up commit (r1781726). With that one the ra-test.exe test which previously deadlocked passes now. However, test 60 (basic_test.py) deadlocks now (svnmucc.exe seems to be the process which is being tested here). I'm planning to details of the underlying issue which I think has now been traced down to the actual root-cause in a blog post most likely tomorrow. That should explain the actual issue in full detail then. Regards, Stefan